Large precast and cast-in-place panels made of cementitious material are widely used in building construction. The panels are typically rectangular in shape. Two panels are positioned with their edges parallel to each other but slightly spaced apart. They are then joined with a steel connector. For example, two precast hollow-core panels are joined with a welded steel connector that is embedded into the interior structure of the two adjacent panels. A number of panels are joined in this fashion to define the walls, floors, and/or ceilings of the building.
Although this approach is widely used, the inventors have recognized that it has shortcomings. The cementitious material provides a highly alkaline chemical environment that can lead to rapid corrosion of the embedded portion of the steel connector. The portion that is not embedded may also corrode. The corrosion of the embedded portion of the steel connector is not visible for routine inspection, so that its extent is not known with certainty.
The steel connector weakens as it corrodes. The weakening leads to a lower strength of the building. The lower strength is of concern, particularly where the building is subject to seismic loadings. A building that is designed and built with adequate strength may become unsuitable where it has been weakened by corrosion of the steel connectors. Repairing and/or retrofitting the building to improve the strength of the connection is difficult, if not impossible, with this connection system.
There is a need for an improved approach to the interconnection of cementitious building panels and other structural building units that achieves acceptable strength but reduces the incidence of corrosion and premature failure. The present invention fulfills this need, and further provides related advantages.
The present invention provides a method for interconnecting building panels of a wide variety of types, and the connected structures. The present approach achieves adequate strength for static and seismic loadings. It also avoids corrosion typically associated with the use of steel interconnectors, and consequently maintains stable strength properties for extended periods of time. The present approach may be used in new construction and in repairing/retrofitting applications with equally advantageous results. It may be used to form walls, floors, and/or ceilings.
In accordance with the invention, a connection is formed between a first building panel having a first-panel face and a first-panel edge of the first-panel face, and a second building panel having a second-panel face and a second-panel edge of the second-panel face. The first-panel edge and the second-panel edge are adjacent to each other with a gap therebetween. The method includes furnishing a connector plate made of a composite material of fibers embedded in a matrix, and connecting the first building panel and the second building panel together using the connector plate. The step of connecting includes the step of affixing the connector plate to the first-panel face and to the second-panel face and extending across the gap between the first-panel edge and the second-panel edge. The gap is filled with a non-brittle material.
The first building panel and the second building panel are each preferably made of a cementitious material. The building panels may be solid or hollow. The building panels may be precast or cast-in-place. The first-panel edge and the second-panel edge are substantially parallel to each other and adjacent to each other, but typically not touching each other. The first face of the first building panel and the first face of the second building panel may be substantially coplanar. Examples include two panels that are part of a wall, two panels that are part of a floor, or two panels that are part of a ceiling. They may instead not be substantially coplanar. Examples include the joining of a wall panel to a floor panel, the joining of a wall panel to a ceiling panel, the joining of two non-coplanar wall panels to make a shaped wall, and the joining of two non-coplanar floor panels (as in a ramp of a parking garage).
Most preferably the connector plate comprises carbon fibers embedded in an organic matrix. The connector plate may be prepared as a plurality of plies of fibers, such as carbon fibers, embedded in an organic matrix. In one approach, the fibers are carbon fibers that are unidirectional within each ply, lie parallel to the faces of the panels, and are oriented at an appropriate angle to the panel edge depending on the panel configuration. Desirably, the angles of the fibers in alternating plies are balanced at +/xe2x88x92xcex1 degrees to the panel edge. That is, in one ply the fibers are oriented at +xcex1 degrees to the panel edge, in the next ply the fibers are oriented at xe2x88x92xcex10 degrees to the panel edge, and so on. In a typical case, xcex1 is about 45 degrees, but the invention is not so limited. An important advantage of the present approach is that the fibers in other plies may be oriented in other directions as well to achieve particular isotropic or anisotropic strength properties as may be needed for particular applications. For example, where out-of-plane bending exists at the panel interface, additional fiber reinforced plastic composite plies may be oriented with the fibers lying parallel to the face of the panel and in the 90-degree direction relative to the panel edge.
It is preferred that the connector plate be installed to cementitious building panels by removing cementitious material, as with a high-pressure water jet, to form a recess in the first building panel and the second building panel so that the connector plate may be received into the recess in the step of affixing. An adhesive material is applied into the recess prior to placing the connector plate into the recess. The connector plate may be affixed to at least one of the first plate and the second plate with an adhesive and/or with an anchor bolt. The adhesive should have a strength of at least about 3600 pounds per square inch (psi) in order to achieve load transfer into the connector plate.
The connector plate desirably overlaps each of the first building panel and the second building panel by an amount sufficient to fully load the fibers in the connector plate. According to calculation, the connector plate preferably overlaps each of the first building panel and the second building panel by an amount Ld of at least about 2tE11e11/f. In this relation, t is the thickness of the fiber reinforced composite connector plate, E11 is the Young""s modulus of the fiber reinforced composite material parallel to a direction of elongation of the fiber, e11 is the maximum tensile strain of the fiber reinforced composite material before failure, and f is the peel off shear strength of the concrete from the first building panel.
The connector plate may be fabricated in place, by a collation, bonding, and curing procedure. Plies of the composite material are furnished and collated to form a multi-ply stack determined to have the required strength properties after curing. The plies are bonded together by curing, either at room temperature or by heating to a curing temperature. This approach allows the connector plate to be custom-made for each pair of building panels. Alternatively, standard connector plates may be fabricated remotely and bonded to the building panels at the construction site. Additional strength is achieved by lengthening the connector plate in the direction parallel to the edges of the building panels, or by using multiple connector plates.
The present approach permits large structures to be fabricated using building panels that are connected together at the construction site with the composite connector plates of the invention. The composite connector plates are not subject to the types of corrosion that weaken conventional steel connectors over time, so that the building strength remains at the initial design level. The composite materials are lighter than steel and may be handled more readily during fabrication. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.